It is a well known principle that the integrity of concrete structures is improved by making sure that the wet concrete poured into the form is substantially homogeneous; that is with the aggregate spread and evenly distributed and substantially all voids or air pockets eliminated. To do this, it is common practice to insert a vibrating head into the wet concrete within the retaining form. As the head is moved up and down and around the form and between the grid of reinforcing bars, pockets of aggregate or voids are eliminated. In my so-pending U.S. patent application Ser. No. 09/233,801, Jan. 19, 1999 and entitled "Concrete Vibrator", now U.S. Pat. No. 6,155,708, issued Dec. 5, 2000, I disclose and claim an improved vibrator that includes such a head and driven by a light-weight gasoline motor connected through a flexible drive cable within a sheath. The vibrator of that patent application represents a substantial improvement over prior art devices in assuring the proper spreading of the aggregate and elimination of the voids in the wet concrete. As disclosed, this desired result is accomplished by providing an intense, reasonably high frequency and amplitude vibration to the concrete from the vibrator head, This prior application is incorporated in the present application by reference.
As set forth in the '801 application, a variety of rotor shapes are disclosed in the prior art. Typically, such as shown in the Lyle U.S. Pat. No. 4,057,222, the rotor is a standard metal bar with approximately one-half removed along the longitudinal axis. The rotor has stub shafts at each end for mounting in a metal casing by dual roller bearings mounted at both ends. A similar arrangement is illustrated in the U.S. Pat. No. 3,042,386 to Wyzenbeek. While this type of mounting has proven successful, additional improvement in the rotor and its mounting is possible. It is particularly desirable to provide enhanced vibration for a particular rotor mass, and without an increase in speed from my previous design, while at the same time assuring that the rotary mounting of the rotor is stable and secure. Improvements in durability, long life and low maintenance cost are also desirable.
Improving the efficiency of the vibration to provide better aggregate spreading and filling of the voids and air pockets has been attacked from many directions in the past. This fact is attested by the concepts shown in the patents described as background in my prior '801 application, and many others. Increasing the intensity of vibration in a concrete vibrator of the type disclosed in the '801 application to accomplish the improved results while maintaining the reduced speed of rotation is important. If successful, such a design change would further enhance the ease and efficiency of use of the concrete vibrator by the worker, thus providing still further increases in productivity and reduction of fatigue during use. At the same time, it is desirable to simplify the eccentric rotor to further reduce the initial cost and to ensure that the maintenance requirements are minimized and the expectant life of the head is extended. Also, a guide line must be that any new vibrator head is adapted for use in the concrete vibrator unit of the '801 application.